Separation of C2F6 from CF4 by adsorption on activated carbon

Details Separation of C2F6 from CF4 by adsorption on activated carbon Separation of C2F6 from CF4 by adsorption on activated carbon

2003-04-08

2003-12-30

Spitzer, Robert H. (Department: 1724)

Gas separation: processes

Solid sorption

Inorganic gas or liquid particle sorbed

C095S097000, C095S142000, C095S901000

Reexamination Certificate

active

06669760

ABSTRACT:

BACKGROUND OF THE INVENTION
Historically, high purity CF
4
, which is used to etch silica in the manufacture of integrated circuits, has been derived by the direct fluorination of carbon. Purification of the CF
4
gas formed, which includes the removal of impurities such as C
2
F
6
, has been effected by temperature swing adsorption using a zeolite bed, such as, NaX (13X). CF
4
is co-adsorbed with the C
2
F
6
impurity on the 13X zeolite. When the bed is saturated with C
2
F
6
, a N
2
purge is passed through the spent adsorbent bed in order to recover some of the coadsorbed CF
4
from the bed. The CF
4
, which is less strongly adsorbed than the C
2
F
6
, desorbs first into the N
2
purge gas and then the C
2
F
6
is desorbed. The N
2
purge gas containing desorbed CF
4
, and small amounts of desorbed C
2
F
6
, is passed through a second bed of 13X zeolite until the C
2
F
6
concentration in the effluent rises to an unacceptable level in the CF
4
/N
2
mixture. By this process about half of the co-adsorbed CF
4
can be recovered before the C
2
F
6
concentration in the effluent becomes too high.
Representative patents relating to the separation of carbon fluoride gases are as follows:
U.S. Pat. No. 6,187,077 discloses a process for separating at least one of CF
4
and C
2
F
6
from a gas containing at least one of NF
3
, CHF
3
and N
2
and SF
6
. The process steps include 1) passing a feed stream containing various impurities through a glassy membrane to produce a retentate stream rich in SF
6
and at least one of CF
4
and C
2
F
6
, and, then 2) contacting the retentate stream with an adsorbent effective to adsorb SF
6
and produce a product stream rich in at least one of CF
4
and C
2
F
6
. Representative adsorbents include zeolites, preferably X types, activated carbons, e.g., BPL, (data sheet indicates a CCl
4
activity of 60-65), PCB (data sheet indicates a CCl
4
activity of 60), BAC, F-300, F-400, BPL, RB2 (data sheet indicates an activity of 65) with PCB being the preferred activated carbon. Polymeric adsorbent resins, and carbon molecular sieves are also disclosed.
U.S. Pat. No. 5,523,499 discloses a process for the purification of C
2
F
6
contaminated with CClF
3
and CHF
3
impurities by adsorption. The C
2
F
6
gas contaminated with impurities is contacted with a sorbent which includes zeolite molecular sieves and activated carbons. Preferred activated carbons, such as BPL from the Calgon Corporation and Type UU from Barneby and Sutcliffe Corp having a particle size of from 4 to 325 mesh.
Japanese Patent Application No. 54-62867 (disclosure 55-154925) discloses a purification process for CF
4
containing CF
3
Cl as an impurity. The process comprises the steps of irradiating the gas stream with a laser and absorbing photons in the fluorine compounds thereby converting the CF
3
Cl to C
2
F
6
and Cl
2
. The C
2
F
6
is then removed via distillation or adsorption.
There is a need in the industry for adsorbents that would allow for a long onstream time for a given column size and a need for adsorbents which have a higher selectivity for carbon fluoride impurities other than the CF
4
product. Such improved adsorbents would enhance the recovery of CF
4
.
BRIEF SUMMARY OF THE INVENTION
This invention relates to an improvement in a process for removing C
2
F
6
as an impurity from a CF
4
containing gas, preferably CF
4
produced by the reaction of F
2
with carbon. The improvement in the process comprises the steps:
contacting said CF
4
containing gas with an activated carbon having a CCl
4
activity from 43 to 55 in an adsorption bed to effect selective adsorption of said C
2
F
6
impurity; and,
recovering a purified CF
4
product in the effluent from said adsorbent bed.
Significant advantages of this process include:
an ability to remove impurities from a CF
4
containing gas stream contaminated with fluorocarbon impurities;
an ability to selectively adsorb contaminant C
2
F
6
without effecting substantial losses to irreversible adsorption of CF
4
;
an ability to provide for long onstream times in the adsorption process; and,
an ability to achieve effective removal of the fluorocarbon impurities from the CF
4
product.


REFERENCES:
patent: 4820318 (1989-04-01), Chang et al.
patent: 5206207 (1993-04-01), Tolles
patent: 5421860 (1995-06-01), Bretz et al.
patent: 5523499 (1996-06-01), Corbin et al.
patent: 5710092 (1998-01-01), Baker
patent: 5814127 (1998-09-01), Li
patent: 5976222 (1999-11-01), Yang et al.
patent: 6017382 (2000-01-01), Ji et al.
patent: 6187077 (2001-02-01), Li
patent: 6224677 (2001-05-01), Nozawa et al.
patent: 54-62867 (1979-05-01), None

Affiliated with

Also associated with

Rating

Separation of C2F6 from CF4 by adsorption on activated carbon does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Separation of C2F6 from CF4 by adsorption on activated carbon, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Separation of C2F6 from CF4 by adsorption on activated carbon will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3120407